1. Field of the Invention
This invention relates to a novel system for separating a solid body from the surface of a resilient member. It utilizes very high repulsive forces to impart rapid expulsive movements to a flexible elastomeric member. The forces are generated by overlapping conductive members that receive a very high instantaneous current pulse from a power storage unit. The forces distend the elastomeric member and separate the elastomeric member from a solid body thereon. The invention is useful for separating ice gathered on a substrate, and it is particularly useful for aircraft deicing applications. It relates to an aircraft deicing system which does not require stretching of the aircraft structural members themselves in order to dislodge the accreted ice. Most especially, it relates to such a system that can be provided as a retrofit on existing aircraft.
2. Description of the Prior Art
Low-altitude, slow flying aircraft such as the helicopter are especially vulnerable to the effects of an icing environment. United States military and civilian helicopters are not currently certified to operate in weather where even light icing conditions might occur. Having all-weather flying capability could greatly expand the utility of the helicopter. A major technological impediment to extending helicopter operations into the all-weather flight regime is that of rotor blade ice accumulation. The sensitivity of the blades to ice accretion is well recognized; however, a satisfactory rotor blade deicing system has heretofor been unavailable.
A wide variety of systems are known in the art for removing ice from aircraft during flight. Examples of such techniques include electrothermal systems, which have a high power demand and are therefore relatively heavy; heated fluids or chemical sprays, which have performance and duration limitations; pneumatic boot systems, which have slow response times and adverse aerodynamic effects; and electromagnetic coils for inducing moving of the structural members themselves, which are of limited practical application, due to material fatigue considerations, size and location restrictions, rigidity of structure, and high power demand. Also, such movement of aircraft structural members often imposes large loads in directions which the structural members are least suited to resist them.
The typical cycle time for a pneumatic deicing system to go from one relaxed state to the next (with an expansion state in between) is close to two minutes. The long expansion period results in aerodynamic degradation. The typical pneumatic deicer is inoperative if the accreted ice layer is thinner than one-quarter inch. When the ice layer is thinner than one-quarter inch, the layer flexes, but does not crack, when the boot is expanded. Aerodynamic performance is obviously impaired when the ice buildup is that great.
The thermal approach to ice removal from airfoils is exemplified by U.S. Pat. No. 1,819,497 to Chrisholm which discloses the use of electrical energy to generate heat in the airfoil surface to melt the ice and to loosen it sufficiently so that it may be blown away. This process requires that a large amount of electric power be dissipated in order to achieve a practical melt period. The electrothermal deicers used on present day aircraft require approximately 12-27 watts/in..sup.2. One military helicopter with a two-blade rotor requires a dedicated 2 kva power supply to operate its electrothermal deicer.
There are numerous references which disclose devices within a airfoil which attempt to break loose ice on the airfoil by deforming the skin of the airfoil. British Patent Specification No. 505,433, Goldschmidt, May 5, 1939, discloses various wing deicers that use internal "hammers" to distort the leading edge of the wing. The wings have either a single or a double-wall leading edge and the "hammers" may be electric, hydraulic or pneumatic. In still another embodiment, electric currents are passed through the inner and outer walls of the wing in order to force apart the walls and deform the wall on which the ice has collected. U.S. Pat. No. 3,549,964 to Levin reveals an aircraft deicer wherein pulses from a pulse generator are routed to a coil (or a spark-gap pressure transducer) adjacent the inner wall of an airfoil. The primary current in the coil induces a current in the wall of the airfoil and the magnetic fields produced by the currents interact so as to deform the wall. U.S. Pat. Nos. 3,672,610 (Levin); 3,779,488 (Levin) and 4,399,967 (Sandorff) disclose additional aircraft deicers that utilize energized induction coils to vibrate or torque the skin on which the ice forms. In each case the electromagnetic coils or magnetrostrictive vibrators are located on the inside surface of the skin that collects the ice. In the Levin et al. electromagnetic inductive deicing system of U.S. Pat. No. 3,809,341 flat buses are arranged one opposite the other with one side of each bus being adjacent an inner surface of an ice-collecting wall. An electric current is passed through each bus so as to force apart the buses and deform the ice-collecting walls. The National Aeronautics and Space Administration funded a program to test an electromagnetic coil deicer system in a Cessna Aircraft Model 206 and the program is described in Aviation Week & Space Technology, July 9, 1984, pages 65 and 66. The right wing of the aircraft was cut open and seven electromagnetic coils were positioned in a row along and near the inner wall of the leading edge. When the coils were energized the metal wall sections adjacent the coils were forced away from the coils and deformed. The deformation caused ice breakage. The deicing systems in these references all suffer a common disadvantage. In order to provide a set level of ice removal, a predetermined skin deflection is required. This deflection requires a large force generation from the electromagnetic system and the price for that force is high fatigue-inducing stress levels in the skin.
In addition to the performance limitations of these prior art systems, a severe limitation common to most of them is that they must be installed at the time an aircraft is built, since retrofitting them would be extremely difficult. Thus, while the art pertaining to aircraft deicing systems is a well developed one, a need still remains for further improvements, particularly for a system that can be easily installed in existing aircraft.
Further, ice accretion on aircraft predominantly initiates, accumulates, and spreads from the frontal areas or so-called leading edges of the structural surfaces. These surface areas are inherently more rigid so as to resist the various imposed air loads, either through increased material thickness, small radius of curvature, or reinforcements, than are the adjacent external skin areas where the airflow is normally parallel and the air loads generally far less. Further, the leading edges of airfoils are usually designed so as to better withstand compressive loads on the external surface as opposed to compressive loads on the inner surface. This characteristic of frontal surface rigidity is even more pronounced in the case of helicopters, where the leading edge of the metal rotors primarily consist of an enclosed D-shaped or elliptically-shaped heavy extruded spar whose wall thickness is typically 3/8" thick at the thinnest wall (not the leading edge wall). In view of the thick rotor wall and the limited empty space normally available within a rotor, a rotor-contained magnetic coil would be a very unsatisfactory means for removing ice from the front surfaces of the rotor.